Liquid pressure control system



June 10, 1941. a M, PARKER I 2,244,894

LIQUID PRESSURE CONTROL SYSTEM Filed Jan. 22, 1938 2 Sheets-Sheet 1 wmvm'e y y M. Par/kel- Z 279... f 92w 7 ATTORNEY June 10, 1941. s PARKER 2,244,89f1

LIQUID PRESSURE CONTROL SYSTEM Filed Jan. 22, 1938 2 Sheets-Sheet 2 INVENTOR ATTORNEY Patented June 10, 1941 UNITED STATES PATENT OFFICE Application January 22, 1938, Serial No. 186,448

reat Britain January 30, 1937 Claims. (01. 60-52) This invention relates to liquid pressure control systems adapted to be used for operation of aircraft retractable undercarriages, fairing doors, bomb release devices and the like, which are assisted in one direction of their movement by the action of gravity or other external forces.

The gravitational force on these devices may well be of such extent that, if they are allowed to fall freely the sudden arresting of their movement at the lowered position may cause a shock sumciently great to produce undesirable stresses in the aircraft framework, thus necessitating a heavier and stronger framework than would otherwise be required. Further, during such a free falling movement, there is a tendency for a. vacuum to form in the liquid pressure system, which may cause air to be drawn in, thus reducing the efliciency of the system.

One object of the present invention is to provide a liquid pressure control system in which the free fall of the operated member under the action of gravity or other external forces is controlled or restricted.

Another object of the invention is to provide a liquid pressure control system comprising a pump having a connection with a. motor and valve means on said connection oifering a greater resistance to the flow of liquid in one direction than to the flow of liquid in the other direction.

Another object of the invention is to provide a liquid pressure control system including a pump and a double-acting motor, and means permitting an unrestricted flow of liquid from the pump to the motor for operating said motor in one direction, and valve means for restricting the flow of liquid from said motor when the latter is operated in an opposite direction.

Yet another object of the invention is to provide a liquid pressure control system including a pump having a connection with a motor, a valve on said connection for restricting the flow of liquid from said motor in one direction, and means for by-passing said valve in the event of the resistance offered to said flow of liquid exceeding a predetermined value.

Other objects and features of the invention and other novel combinations of parts and desirable particular constructions will be apparent from the following'description and from the accompanying drawings, in which:

Figure 1 is a diagrammatic view of a liquid pressure control system in accordance with my invention, shown in association with an aircraft retractable undercarriage;

Figure 2 is a section on an enlarged scale of shown in Figure 4.

Referring to the drawings, Figure 1 shows, diagrammatically, an aircraft undercarriage comprising a shock absorber leg I pivoted at 2 to the front wing spar 3 of an aircraft, and a folding strut consisting of two portions 4 and 5 extending between the leg I and an attachment point 6 on the rear wing spar l. A liquid pressure operated jack 8 is mounted between the upper part 5 of the strut near the joint ll of the two parts, and a second attachment point l2 on the rear wing spar l.

The jack 8 is of the double acting type, and is operated by liquid pressure generated by a pump I3 driven by the engine of the aircraft. The pump l3 draws liquid from a reservoir H, and delivers it to a selector valve l5, which may be set to connect the pump delivery to either of two conduits l6 and H, the former of which leads to the upper end of the jack 8, and so conveys liquid thereto for the purpose of lowering the undercarriage, whilst the latter, ll, conveys liquid to the lower end of the jack to raise the undercarriage. It is of course obvious that the conduit which, during any particular operation is not delivering liquid to the jack, is being traversed by llquid returning from the low-pressure side of the jack to the reservoir.

On the conduit I! is mounted a valve means I 8, consisting of two non-return valves 2|, 22 opening in opposite directions.

The inlet valve 2| opens when liquid travels from the pump I3 to the jack 8 to raise the undercarriage, the outlet valve 22 being then held firmly on its seat by the pressure. The valve 2| has only a light spring tending to hold it on its seat, and there is therefore practically no restriction to the flow of liquid entering the jack to shorten it and produce retraction of the undercarriage.

The inlet valve 2| is of course held on to its seat when liquid is returning from the jack to the reservoir by the conduit H, and the outlet valve 22 has to open to allow such liquid to pass. This outlet valve 22 is loaded by a strong spring,

so that a considerable pressure must be createdin the liquid before this valve opens.

In retractable undercarriages, movement from the retracted to the extended position is of course assisted by the action of gravity, and the valve means according to my invention controls the movement of the undercarriage when it is being so assisted, to prevent the undercarriage from running away from the operating pressure. The loading of the outlet valve may of course be so arranged that the weight of the undercarriage is just suificient to overcome the resistance, and the undercarriage falls slowly under its own weight, or this valve may be so loaded as entirely to prevent downward movement of the undercarriage under its own weight, it being necessary to create pressure in the upper end of the jack for the lowering operation.

Figure 2 is a detailed view of valve means l8 shown in Figure 1. The valve means is inserted in the conduit H, the two sections of which are connected to the unions 23 and 24. The latter are connected internally by a direct passage 25 in which is mounted the lightly loaded ball valve 2|, co-operating with a seat 26. This valve is loaded on to the seat 26 by a light spring 2'! taking its support at 28 on the inner part of the union 24. On each side of the valve 2| are connected transverse passages 3|, 32, connected by a further bore 33 parallel to the direct passage 25. In the bore 33 is a valve seat 34 on which seats the outlet ball valve 22, loaded by a spring 35 the strength of which is selected to give the necessary resistance to lowering of the undercarriage. This spring is adjustable by means of an abutment screw 36 locked in position by a cap nut 31, to vary the loading of the valve.

An alternative form of valve means is shown in Figure 3, consisting of a casing 38 having unions 4|, 42 for connecting it to the conduit I! (Figure 1), and having a chamber 43 in which is movably mounted a plate 44.

The two unions 4|, 42 are connected to ports 45 and 46 in the opposite end walls of the chamber 43, the port 46 connected to the union 42 on the side or the valve nearer to the jack being of greater area than the port 45. The plate 44 has a central aperture 4'! which registers with the .port 45, but is of less area than this port, and a series of supplementary apertures 48 arranged around a circle and which come within the area of the port 46 but are outside the area of the .port 45. The flow of liquid in the conduit causes the plate 44 to bear against the wall of the chamber 43 opposite to that through which the liquid is entering. Consequently, when liquid is being supplied to the jack to raise the undercarriage, the plate 44 is held against the wall of the chamber 43 containing the port 46, and liquid can flow through all the apertures 41 and 46, giving a free flow. Liquid returning from the jack to the reservoir when the undercarriage is being lowered moves the plate 44 into engagement with the other wall of the chamber 43, thus shutting ofi the apertures 48, and leaving only the aperture 41 open, and causing a restriction of flow which depends on the area of the aperture 41.

The valve means shown in Figures 4 and is similar to that shown in Figure 2, but has incorporated therein a by-pass which is opened when a predetermined pressure is reached in the system, to by-pass the heavily loaded outlet valve, and allow the full pressure generated by the pump to be usefully employed in the movement of the undercarriage. This by-pass is an extremely desirable feature in cases where the whole extending movement of the undercarriage is not assisted by gravity, or where, in the later stages of lowering, the effect 01 gravity on the undercarriage is counterbalanced, or more than counterbalanced by the resistance of the airstream, or where a lock has to be engaged or disengaged at the end or beginning of the undercarriage movement.

This device comprises a casing 5| in which are mounted unions 52, 53 for connection to the two .parts of the conduit (Figure 1). These unions open into parallel passages 54, 55 in the casing 5|, which passages are connected near their ends by cross passages 56, 51. The passage 56 contains the lightly loaded inlet valve 58, which is urged towards a seat 6| by a spring 62 taking its abutment on a plug 63. The passage 5'! contains the heavily loaded outlet valve 64, urged towards its seat 65 by a spring 66 whose compression is adjustable by means of a plunger 61 and screw-threaded sleeve 68, the plunger being positioned relatively to the sleeve 68 by a pin extending through registering holes formed in said sleeve.

The pin 1| provides a releasing device for the outlet'valve, removal of the pin taking oil the load from the spring 66 and so freeing the valve 64. The primary object of this is to enable the entire removal of the resistance oflered to the flow of liquid in the event of failure of the engine driven pump, which normally generates the pressure in the system, so that operation by an auxiliary hand pump may be facilitated.

In the casing 5| formed with passages 54, 55 and passages 56, 51, is formed a bore 72 having its axis at right angles to the general plane of these passages, and a valve member 13, having an annular groove 14, is slidably mounted in said bore. Ports 15, I6 connect the passagm 54, 55 to the bore 12 at spaced points along its length, and these ports arefdisconnected or'connected by movement of the valve member 13 in the bore, said ports being connected when both of them are in register with the annular groove 14. Adapted to abut one end of the valve member I3 is a piston I1 fitting in a cylinder 18 formed by a reduced extension of the bore 12, and the other end of said valve member is loaded by a spring I9, adapted to be adjusted by means of a thimble 8| threaded into a sleeve 82 itself mounted in the end of the casing 5|.

The operation of this device is similar to that of the valve means described with reference to Figures 1 and 2, the valve member 73 being normally in such a position that the port 15 is disconnected from the .port 16. The cylinder 18 is connected by a union 83 and branch conduit to the conduit l6 of Figure 1, so that the pressure in that conduit during lowering of the undercarriage acts on the piston 11, tending to move the valve member 13 to the right of Figure 5. The spring 19 may be of any selected strength, so that the valve member 13 is moved when the load reaches a predetermined limit to by-pass the outlet valve 64 and permit the full pressure generated by the pump to act on the undercarriage jack.

So long as the undercarriage is extending easily, very little pressure exists in the conduit l6,

and the outlet valve 64 remains in action to control such extension.

If however a resistance to extension is met,

as for example when the undercarriage reaches a position in which gravity no longer assists its movement, the presure rises until it acts on the piston II with suilicient force to compress the spring It. and move the valve member 13 to bring the ports I! and Il into communication with each other, thus allowingliquid to flow from the jack to the reservoir without restriction, and permitting the full pump pressure to be usefully used to complete the extension of the undercarriage,

It will be understood that the higher pressure may be necessary at the commencement of the extension of the undercarriage, for example to release a look. In this case the valve member 13 will be moved to connect the ports 15 and 16 before the undercarriage is released, and as soon fective for restricting the flow of liquid from the motor when the piston is operated in the opposite direction, said first-named means comprising a non-return valve permitting flow of liquid in said one direction, and wherein the means for restricting liquid flow comprises a heavily loaded non-return valve connected in parallel with the as the undercarriage is released and its weight begins to assist theextension, the fall of pressure in the conduit It will allow the spring I! to return the valve member II to a position in which the port 53 is disconnected from the port 52, and the outlet valve will come into action.

Although this invention has been described in connection with certain specific embodiments, the principles involved are susceptible of numerous other applications which will readily occur to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described the various features of the invention, what I claim as new and desire to secure by Letters Patent is- 1. A liquid pressure control system including a pump, a reservoir, a motor having a piston movable therein first in one direction and subsequently in the opposite direction; connections between the pump, the reservoir and the motor, means for rendering said connections eflective to produce unrestricted flow of liquid into the motor for operating the piston in one direction, additional means for rendering said connections eifective for restricting the flow of liquid from the motor when the piston is operated in the opposite direction, and means for by-passing the restrictingmeansinresponsetoapressurerise behind the piston during any stage of piston movement in said opposite direction.

2. A liquid pressure control system including apump,areservoir,amotorhavingapiston movable thereiniirstinonedirectionand subsequently in the opposite direction, connections between the pump, the reservoir and the motor, means of rendering said connections effective to produceunrestrictednoworliqmdintothemotor for operating the piston in one direction, additional means for rendering said connections effirst valve and controlling flow of liquid in the opposite direction, and means for by-passing the heavily loaded valve, said by-passing means including a third valve and means responsive to a pressure rise behind the piston, as it advances in said opposite direction, to shift said valve to a liquid by-passing position.

3. A liquid pressure control system including a pump, a reservoir, a motor having a piston movable therein first in one direction and subsequently in the opposite direction, connections between the pump, the reservoir and the motor, means for rendering said connections effective for restricting the flow of liquid from the motor when the piston is operated in one direction, and means operated by a pressure rise behind the piston, during any stage of piston movement in said one direction, for by-passing the restricting means.

4. A liquid pressure control system according to claim 1, wherein the means for producing unrestricted flow of liquid to operate the piston in one direction comprises a lightly loaded nonretum valve permitting a practically unrestricted flow of liquid in one direction, and wherein the flow restricting means comprises a heavily loaded non-return valve connected in parallel with the first valve and controlling a flow of liquid in the opposite direction, and means for by-passing the heavily loaded valve in response to a pressure rise on the side of the piston which is remote from said heavily loaded valve.

-5. A liquid pressure control system including a pump, a reservoir, a double acting motor, the latter having a piston whose movement in one direction is aided by gravitational forces and whose movement in the opposite direction is opposed by gravitational forces of a magnitude which varies as the piston progresses on its stroke, connections between the pump, the reservoir and the motor, said connections including valve means located in those parts of said connections through which the fluid must flow on its journey therethrough, and means acting upon said valve means to vary the total effective cross-sectional area of flow through said valve means. and hence the rate of discharge of fluid from said motor tosaidconnectionsasthepistonprogressesin the direction in which its movement is aided by gravitational forces.

SYDNEY MACDONALD PARKER. 

